Hi everyone out there
Regarding the use of normal dual inlet machines for enriched
experiments, I want to say that Andrew is proposing works. I found out
it some years ago in a more experimentally way. I had to measure
samples from a field experiment using D2O like a tracer, so, trying to
measure DH in my mass spec I saw that the only way to balance was
using cup 3 (which the highest intensity beam), instead of (as usual)
cup 2. Then I used one enriched sample from the experiment itself like
my reference gas and  finally was able to pesent my results as
absolute ratios against that sample defined like my zero. My results
were in the form of a perfect Gaussian curve similar to others found
in the same study using  chemical (not isotopic)  tracers. Of course I
was not able  to give the results in delta notation vs international
standards but it did not matter in this case.
I hope this helps
Dr. Rafael Nun~ez Gomez
NERC Isotope Geosciences Laboratory
British Geological Survey
Nicker Hill,  Keyworth
Nottingham, NG12 5GG
UK
Tph: 00 44 115 9364143
email: [log in to unmask]